U.S. patent application Ser. No. 09/030,863, filed on Mar. 31, 1997 and entitled "Glass-Ceramics," the disclosure of which is incorporated herein by reference in its entirety, disclosed materials that can be used as substrates for high temperature polysilicon thin films. The transparent glass-ceramic materials disclosed in Ser. No. 09/030,863 have high strain points and coefficients of thermal expansion which are compatible with polycrystalline silicon, especially high temperature poly-Si. The glass-ceramics disclosed in Ser. No. 09/030,863 have expansions that were designed to closely match that of silicon (C.T.E. of 32-42.times.10.sup.-7 /.degree. C.).
It would be desirable to provide glass ceramics having high strain points, and in addition, having thermal expansion characteristics that are intermediate between those of silica and of silicon. Glass-ceramics having a thermal expansion below about 32.times.10.sup.-7 /.degree. C. over the temperature range of 25-1000.degree. C. and having strain points in excess of 850.degree. C. can be preferable in various applications. It would also be advantageous to provide a glass-ceramic having a low density in combination with the low thermal expansion and high strain point.